Uncontrolled production of a hydrocarbon reservoir may result in a coning effect, meaning that a producing zone of the reservoir starts producing water. Water mobility into a geological formation is higher than oil mobility. As a consequence, once the production of water has started it is extremely difficult to recover most of the oil still in the producing zone of the reservoir. Thus, improving oil recovery from a hydrocarbon reservoir requires the implementation of a proper reservoir management. Downhole equipments are used to control the production rate of at least one producing zone PZ of a reservoir GF into a cased well bore WB and/or production tubing PT towards the surface ST as depicted in FIG. 1. Further, downhole equipments are also used to shut off or limit the production of a zone if it produces water in multi producing zones situation. Typically, such downhole equipments comprise downhole flow control valves FCV that are able to lower or stop the production rate of a producing zone. A flow control valve can be either a two-position valve or a multi-position valve. A two-position valve can be full open or full close. A multi-position valve has intermediate positions such as to control the flowing rate from a full open state to a full close state. Generally, the flow control valve is coupled to sensors giving measurements of, for example, pressures, temperatures and types of fluid flowing out of the producing zones. These measurements are transmitted to equipments and operators at the surface ST.
Typically, a flow control valve is based on the principle of a sliding sleeve covering or uncovering a series of holes of the production tubing. The position of the sleeve is adjusted in order to open or close, entirely or not, the flow control valve. Generally, the flow control valve is hydraulically controlled. The displacement of the sliding sleeve is realized thanks to double effect piston with hydraulic pressure coming from the surface. The sliding sleeve is operated upward or downward, depending on the target position to reach. In order to know at any time the position of the downhole valve, a valve position sensor is necessary because the hydraulic control of the valve as above described does not offer a direct feedback of the downhole valve position. Document WO 2007/102821 describes a well tool having a magnetically coupled position sensor. In operation of the well tool, relative displacement is produced between members of the well tool. A magnetically coupled position sensor includes one magnet assembly attached to a member for displacement therewith and another magnet assembly movably attached to the other member and magnetically coupled to the first magnet assembly for displacement therewith. The position sensor further includes a magnetically permeable material which increases a magnetic flux density between the magnet assemblies. The magnetically permeable material may be positioned between magnets of the magnet assemblies and/or spaced apart therefrom.
Implementing such a position sensor inside a flow control valve is difficult because it requires a sensor of a compact size, easy to package and also protected from the harsh downhole oil and gas environment. Further, a position sensor having a compact size is not adapted to the long stroke of the sliding sleeve of the flow control valve.